1. Field of the Invention
The present invention relates to thermoplastic materials having incorporated into or onto such thermoplastic materials a novel antiblocking material and to novel lubricating oil compositions containing such thermoplastic materials.
2. Description of the Prior Art
It is known that certain thermoplastic materials, particularly those having low softening points, often exhibit blocking tendencies or the tendency of the contact points or surfaces of such materials to stick or adhere together during further processing, transport, storage, use etc. For example, thermoplastic materials, in divided form such as pellets, chips, crumbs, etc., are often further processed to incorporate therein solid filler materials, such as carbon black, coloring agents or the like. To the extent that the thermoplastic materials tend to form into lumps or a single solid mass it becomes difficult, time consuming and expensive to evenly disperse the solid material throughout the thermoplastic material. Further, certain polymers are supplied to the end user in the form of films, sheets, slabs, rolls, pellets or powder and, to the extent that thermoplastic material has a relatively low softening point, blocking occurs during shipment and storage. The extent of such blocking will depend upon the particular physical properties of the polymer itself as well as its form. Such variables as temperature, pressure and humidity can also alter the degree to which the polymer exhibits the tendency to block. An increase in any of these variables will generally increase the degree to which the polymer exhibits the tendency to block. Blocking of polymeric materials, especially during storage at ambient temperatures or above ambient temperatures, is therefore a serious problem in the industry.
It is often the desire of commercial users of thermoplastic materials to have these materials available in powder form, i.e. very small particles. Powder-form polymers are particularly desirable to commercial users whose process involves dissolving the polymer in a suitable solvent prior to the polymer's introduction into the manufacturers production process, since the time required to dissolve the polymer is typically directly proportional to the particle size. The cost of grinding equipment and the time required to convert the polymer to powder form is often prohibitive for the commercial user. Furthermore storage space requirements for the producer and user are often reduced if the polymer is in powder form, and shipping costs are similarly reduced compared to the polymer being in a form having a lower bulk density. As desirable as it might be to have powder-form thermoplastic materials available, as previously indicated, the blocking tendency of thermoplastic materials in this form is even more serious than in other forms.
It is also known in the art that the viscosity of lubricating oils, particularly mineral lubricating oils, varies with the temperature. Accordingly, it is usually necessary to add to the lubricating oil a material to increase the viscosity index of the oil. The higher the viscosity index the less the change in viscosity with change in temperature. The viscosity at 210.degree. F. (99.degree. C.) and at 100.degree. F. (38.degree. C.) is used to determine the viscosity index. It has been previously suggested that certain linear and block copolymers when added to lubricating oils in very small amounts are excellent viscosity index improvers. For this use it is desirable that the thermoplastic material be supplied in powder form, thereby facilitating incorporation of the thermoplastic material in the oil. To the extent that the viscosity index improving polymer has a tendency to block during transportation and storage serious problems are encountered since it is necessary to reconvert the polymer to powder form. Grinding equipment is often not possessed by the small lubricating oil compounder and the time required to convert the polymer to powder form is often prohibitive for the commercial user. Consequently, it is highly desirable that such polymeric viscosity index improvers be available in nonblocking powder form.
Various antiblocking agents, i.e. substances that reduce blocking when incorporated into the polymer are applied to the surface of the polymer have been previously employed.
Compounds such as sodium stearate, polyethylene, sodium dioctyl sulfosuccinate, alkyl amines, hydrocarbon esters of phosphoric acid, and alkyl quaternary ammonium compounds have heretofore been employed in particular polymers and are usually incorporated into the polymer before extruding, molding or casting, etc. It is known that specific antiblocking agents can usually be employed only with particular polymers or types of polymers as these substances may not be compatible with the polymer or may adversely affect other desired properties thereof.
Other compounds such as talc, silica, clay, starches, microcrystalline waxes and long-chain alkyl quaternary ammonium compounds have also been employed by applying these materials to the surface of the polymer either during or after extrusion, molding, or casting in order to reduce blocking.